Survey of caesium-137 and strontium-90 in the lower part of the stream

A higher deposition of 137Cs than in the surroundings has earlier been recognised in the lower part of the stream Verkmyrån which is the outlet from the lake Hille. In this study, this area with a higher deposition is examined with a portable gamma spectrometer connected to a GPS backpack. Five different areas were recognised and measured, an alder forest, a spruce grovee within the alder forest, which had showed higher 137Cs levels than the surrounding alder forest, two reed areas and a coniferous forest. The results show that elevated levels of 137Cs are found in the alder forest and the reed areas which were all adjacent to the stream. In these areas, the deposition varied between 500-1500 kBq/m2. In the coniferous forest nearer the alder forest but further away from the stream, the deposition was 200 kBq/m2. Soil samples from the different areas were also taken and sectioned before analysis of 137Cs and 90Sr. The same big difference in the deposition as for 137Cs was not seen or 90Sr in the different areas, the 90Sr deposition varied between 1.5-3.5 kBq/M2. Vertical distribution profiles were plotted for the two radio nuclides and the results show that 137Cs and 90Sr have almost the same distribution pattern with a peak in activity at ~ 5 cm depth. The conclusion from this survey is that the elevated levels of 137Cs in the vicinity of the outlet of the stream Verkmyrån come from redistribution from the lake Hille, primarily in 1986. 90Sr was not redistributed from the lake to the wet land at the outlet in the same amount as 137Cs.